1. Field of the Invention
This invention relates to processes for cleaning vessels, particularly those used for the storage and/or transportation of chemicals and other such materials, in an environmentally and economically acceptable manner. More particularly, this invention relates to a process for cleaning the interiors of a vessel contaminated with chemical residue by washing with solvents, recovering the contaminated solvents for subsequent reuse, and recovering the contaminant for environmentally-acceptable disposal.
2. Prior Art
In the transportation of commodities in tanks, which may be hauled over highways, by tank trucks, over railways by tank cars, over waterways by ships and barges or transported in drums, it is generally necessary and/or desirable at some point in time that the interior of the tanks be thoroughly cleaned of chemical residue. Cleaning is particularly important when the tank is to be refilled with a different commodity, in order to insure against contamination by the residue contained in the tank from the previous load. Cleaning of such tanks is also performed prior to any repair or testing of the tank.
It is estimated that there are hundreds if not thousands, of different commodities which are handled by rail tank cars, tank trucks and drums. Rail tank cars, and some tank trucks and drums, are generally in dedicated service (carrying one commodity only), and unless contaminated, are cleaned only prior to repair or testing. Non-dedicated tank trucks and drums are cleaned after every trip to prevent cross-contamination. It has been estimated that approximately 37,000 rail tank cars, 5 million tank trucks and 25 million drums are cleaned per year (see U.S. Department of Commerce, National Technical Information Service PB-280 726 "Source Assessment: Rail Tank Car, Tank Truck, and Drum Cleaning, State of the Art" by Monsanto Research Corp., Dayton, Ohio, April, 1978).
Due to the wide variety of chemical residues which must be cleaned from such tanks, it is very difficult to design and operate in any environmentally and economically acceptable manner, a single tank cleaning station which can handle such residues.
Generally, the processes for cleaning such tanks utilize cleaning agents such as steam, water, detergents and solvents. These agents, generally, are applied using steam hoses, pressure wands, or rotating spray heads placed through the opening in the vessel. Chipping and scraping of hardened or crystallized products is frequently required. Vapors from tanks used to store volatile materials may be sent to flares at such cleaning facilities. Vapors of materials such as anhydrous ammonia and chlorine are dissolved in water and become waste water constituents. Vapors not flared or dissolved in water are dissipated to the atmosphere.
The steaming, washing and/or flushing of rail tank cars, tank trucks and drums generally results in air emissions and waste water effluents containing pollutants. Air emissions from the cleaning of rail tank cars and tank trucks are both organic and inorganic vapors. Water pollutants from cleaning of rail tank cars, tank trucks and drums are primarily oil, greases, high oxygen demand (COD), suspended solids, and toxic or odorous materials. By EPA estimates, 2/3rds of the tank truck industry discharges waste water effluent to municipal systems with little or no pretreatment. Where such pretreatment has been provided it is generally limited to sedimentation, neutralization and evaporation ponds and lagoons.
Until the late 1960's, little attention was given to waste water treatment from cleaning rail tank cars, tank trucks, and drums. This inattention was primarily due to the fact that the waste waters were generally low in volume, installations were small, and the environmental impact considered relatively minor compared to other industrial pollution sources. As indicated, waste water from an estimated 2/3rds of the installations were directed to municipal treatment systems, the rest were discharged directly to surface water streams with perhaps some oil separation treatment.
In recent years, the tank cleaning industry has been making an effort to improve waste treatment capabilities. No installation is known to have a completely satisfactory treatment system. Applicable state-of-the-art treatment technology is, for the most part, well known and has been used by manufacturing industries for several years. It has been thought that due to the wide variety of residues to be cleaned and the diversity of waste material streams that the use of a single specific process and installation for cleaning was impractical. For this reason, tank car and tank truck cleaning companies have been approaching their individual cleaning and pollution problems by using one or more combinations of methods. To date, however, there is no single practical and economical method for effectively cleaning and reducing the emission from rail tank car and tank truck cleaning operations.
Numerous processes and apparatus have been developed for the cleaning of vessels such as tank trucks, and rail tank cars and drums, see for example the following U.S. Patents:
U.S. Pat. No. 4,106,950 to Grismer--issued Oct. 28, 1977;
U.S. Pat. No. 3,434,881 to Smith--issued Mar. 25, 1969;
U.S. Pat. No. 3,281,269 to Watts--issued Oct. 25, 1966;
U.S. Pat. No. 3,188,238 to Lyon--issued June 8, 1965;
U.S. Pat. No. 3,046,163 to Kearney et al.--issued July 24, 1962;
U.S. Pat. No. 3,042,553 to Kearney et al.--issued July 3, 1962;
U.S. Pat. No. 3,033,215 to Miller--issued May 8, 1962;
U.S. Pat. No. 3,025,190 to Groom et al.--issued Mar. 13, 1962;
U.S. Pat. No. 3,944,924 to Sven-Erik Wiklundh et al.--issued July 12, 1960;
U.S. Pat. No. 2,092,321 to McFadden--issued Sept. 7, 1937;
U.S. Pat. No. 2,065,462 to Olsson--issued Dec. 22, 1936;
U.S. Pat. No. 2,045,752 to Butterworth--issued June 30, 1936;
U.S. Pat. No. 1,816,954 to Byerley--issued Aug. 4, 1931; and
U.S. Pat. No. 1,722,211 to Guardino--issued July 23, 1929.
None of the foregoing references appear to specifically describe a completely environmentally and economically acceptable process for cleaning chemical residues from vessels.
Some of the processes describe, in a general manner, reclaiming and reuse of solvents, see for example, Grismer and Smith, but they do not describe any specific economically and environmentally acceptable process for such reclamation, considering the wide variety of chemical residue or contaminants in the solvents.
Other references describe the use of complicated apparatus for cleaning the interiors of tanks, see for example, Watts.
Other references describe the use of portable cleaning apparatus for cleaning tanks in transit, see for example, Lyon, but say nothing about the waste treatment of the effluent from such cleaning processes.
Other processes describe the use of, for example, chlorinated hydrocarbon solvents in the vapor state of cleaning the interiors of tanks, see for example, both Kearney et al. references. Such processes require complicated heating and spraying equipment.
Most of the references also require the selection of a specific solvent to clean a specific chemical residue and utilize large quantities of such solvents.